public class test05 {
    /**
     * Definition for a binary tree node.
     * public class TreeNode {
     *     int val;
     *     TreeNode left;
     *     TreeNode right;
     *     TreeNode() {}
     *     TreeNode(int val) { this.val = val; }
     *     TreeNode(int val, TreeNode left, TreeNode right) {
     *         this.val = val;
     *         this.left = left;
     *         this.right = right;
     *     }
     * }
     */
        public TreeNode trimBST(TreeNode root, int low, int high) {
            if(root==null){
                return null;
            }
            if(root.val>high){
                return trimBST(root.left,low,high);
            }else if(root.val<low){
                return trimBST(root.right,low,high);
            }
            root.left = trimBST(root.left,low,high);
            root.right = trimBST(root.right,low,high);
            return root;
        }
}
